Vertical parallel plate capacitor structures

ABSTRACT

Vertical parallel plate (VPP) capacitor structures that utilize different spacings between conductive plates in different levels of the capacitor stack. The non-even spacings of the conductive plates in the capacitor stack decrease the susceptibility of the capacitor stack of the VPP capacitor to ESD-promoted failures. The non-even spacings may be material specific in that, for example, the spacings between adjacent conductive plates in different levels of the capacitor stack may be chosen based upon material failure mechanisms for plates containing different materials.

FIELD OF THE INVENTION

The invention relates generally to integrated circuit fabrication and,in particular, to vertical parallel plate capacitor structures for usein integrated circuits.

BACKGROUND OF THE INVENTION

Capacitors are passive elements that are extensively used in integratedcircuits for storing an electrical charge. Capacitors, which includeconductive plates separated by an insulator, have a capacitancecontingent upon a number of parameters, such as plate area, intra-platespacing, and the insulator's dielectric constant. Capacitors are foundin filters, analog-to-digital converters, memory devices, controlapplications, and many other types of integrated circuits, and may beused for electrostatic discharge (ESD) protection.

One common type of capacitor found in integrated circuits is a verticalparallel plate capacitor (VPP). In particular, VPP capacitors may beintegrated into an integrated circuit during back end of line (BEOL)processing forming the stacked metallization layers of multi-levelinterconnect structures or otherwise formed using BEOL processtechniques and materials. Copper metallurgy, which has a higherconductivity than aluminum metallurgy, is used in lower metallizationlayers of the interconnect structure to increase signal propagationspeed. However, aluminum metallurgy is preferred in upper metallizationlayers of the interconnect structure because of the recognizedadvantages of aluminum metallurgy over copper metallurgy for chip andpackage solder and wire bonding connection pads.

Consequently, the plates of VPP capacitors may have either an aluminummetallurgy or a copper metallurgy. As an artifact of the BEOLprocessing, the sidewalls and bottom of each copper plate is lined by abarrier layer. In contrast, aluminum plates are clad on only the top andbottom by barrier layers. Under ESD testing and during ESD events in anoperating device, aluminum plates have been demonstrated to be moreprone to failure than copper plates. Generally, ESD-promoted failure mayoccur by crack initiation and propagation in the dielectric materialbordering the plate followed by melting and flow of the aluminum orcopper from the plate into the crack. Because of the confinement byrefractory metal cladding on the top and bottom surfaces, aluminumplates fail by a lateral cracking mechanism. In contrast, copper platesare confined by refractory metal cladding on the sidewalls and bottomsurface and, consequently, fail in a vertical direction.

VPP capacitors are needed that exhibit increased resistance toESD-promoted failures either during testing or during device operation.

SUMMARY OF THE INVENTION

Embodiments of the invention are generally directed to vertical parallelplate (VPP) capacitor structures that utilize different spacings betweenconductive plates in different levels of the capacitor stack. Thenon-even spacings of the conductive plates in the capacitor stackcontribute to a high electrostatic discharge (ESD) robustness. Thenon-even spacings may be material specific. For example, the spacingsbetween conductive plates in different levels of the capacitor stack maybe chosen based upon material failure mechanisms for conductive platesof different materials. As a more specific example, the capacitor stackof the VPP capacitor may include copper plates with minimum spacingsbetween copper plates and aluminum plates with wider spacings betweenaluminum plates. The wider spacing for the aluminum plates may alleviateESD-promoted failures of the VPP capacitor structures fabricated fromaluminum and copper using back end of line (BEOL)-type processes.

In one embodiment, the capacitor structure comprises a first pluralityof conductive plates and a second plurality of conductive plates havingan overlying relationship with the first plurality of conductive plates.The first plurality of conductive plates are spaced apart by a firstdistance. The second plurality of conductive plates spaced apart are bya second distance different than the first distance.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is cross-sectional view of portions of a substrate carrying avertical parallel plate capacitor structure constructed in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

With reference to the FIGURE, a vertical parallel plate (VPP) capacitorstructure, generally indicated by reference numeral 10, is carried on asubstrate 12. Substrate 12 may include various circuits and/or devices(not shown) formed thereon and/or therein with features that are to becontacted. Substrate 12 may be a semiconductor wafer composed of asemiconductor material including, but not limited to, silicon (Si),silicon germanium (SiGe), a silicon-on-insulator (SOI) layer, and otherlike Si-containing semiconductor materials. Alternatively, substrate 12may comprise a ceramic substrate, such as a quartz wafer or an AlTiC(Al₂O₃—TiC) wafer, or another type of substrate known to a person havingordinary skill in the art.

The VPP capacitor structure 10 includes a capacitor stack defined by aplurality of metallization layers 14, 16, 18 that are formed by back endof line (BEOL) process techniques. Metallization layer 14 includes aplurality of conductive strips or plates, of which conductive plates 20,22 are representative, that are formed in an insulating layer 24.Similarly, the underlying metallization layer 16, which is disposedbetween metallization layer 14 and metallization layer 18, includes aplurality of conductive strips or plates, of which conductive plates 26,28 are representative, that are formed in an insulating layer 30. Aninsulating layer 32 is disposed between conductive plates 20, 22 and 26,28. Conductive plugs, such as the representative conductive plugs 34,36, fill vias defined in insulating layer 32. Conductive plug 34supplies a vertical connection and electrical and physical couplingbetween conductive plate 20 and conductive plate 26. Conductive plug 36supplies a vertical connection and electrical and physical couplingbetween conductive plate 22 and conductive plate 28. Optional additionalplugs (not shown) constructed like plugs 34, 36 may be provided toestablish multiple points of electrical and physical coupling betweenconductive plates 20, 22 and conductive plates 26, 28, respectively.

In certain embodiments, one or more upper metallization layers (notshown) may be disposed in an overlying relationship with metallizationlayer 14. Conductive plugs, such as the representative conductive plugs38, 40, fill vias defined in an insulating layer 42 overlying insulatinglayer 24 and conductive plates 20, 22. Conductive plug 38 may supply avertical connection and electrical and physical coupling betweenconductive plate 20 and a conductive plate in an overlying metallizationlayer. Conductive plug 40 may supply a vertical connection andelectrical and physical coupling between conductive plate 22 and aconductive plate in the overlying metallization layer. Optionaladditional plugs (not shown) constructed like plugs 38, 40 may beprovided to establish multiple points of electrical and physicalcoupling between conductive plates 20, 22 with any overlying conductiveplates.

Metallization layer 18 is disposed below metallization layer 16 and,therefore, between metallization layer 14 and the substrate 12.Metallization layer 18 includes a plurality of conductive strips orplates, of which conductive plates 44, 46 are representative, that areformed in an insulating layer 48. An insulating layer 50 is disposedbetween the conductive plates 26, 28 in metallization layer 16 andconductive plates 44, 46 and, therefore, between insulating layers 30and 48. Conductive plugs, such as the representative conductive plugs52, 54, fill vias defined in insulating layer 50 to supply respectivevertical connections and electrical and physical couplings betweenconductive plates 26, 28 and conductive plates 44, 46, respectively.Optional additional plugs (not shown) constructed like plugs 52, 54 maybe provided to establish multiple points of electrical and physicalcoupling between conductive plates 26, 28 and conductive plates 44, 46,respectively.

In certain embodiments, additional lower metallization layers (notshown) may be disposed between metallization layer 16 and substrate 12.Conductive plugs, such as the representative conductive plugs 55, 56,fill vias defined in an insulating layer 58 underlying insulating layer48 and conductive plates 44, 46. Conductive plug 55 may supply avertical connection and physical coupling between conductive plate 44and a conductive plate in an underlying metallization layer. Conductiveplug 56 may supply a vertical connection and physical coupling betweenconductive plate 46 and a conductive plate in the underlyingmetallization layer. Optional additional plugs (not shown) constructedlike plugs 55, 56 may be provided to establish multiple points ofelectrical and physical coupling between conductive plates 44, 46,respectively, and any underlying conducting plates.

The insulating layers 24, 32, 42, 48, 50, 58 may be deposited by aconventional technique, such as a chemical vapor deposition (CVD)process or a plasma enhanced CVD (PECVD) process, understood by a personhaving ordinary skill in the art. The insulating layers 24, 32, 42, 48,50, 58 may comprise silicon dioxide, fluorine-doped silicon glass (FSG),combinations of these dielectric materials, and other dielectricmaterials recognized by a person having ordinary skill in the art.

Suitable materials for conductive plates 20, 22, 26, 28, 44, 46 of theVPP capacitor structure 10 and conductive plugs 34, 36, 38, 40, 52, 54,55, 56 include, but are not limited to, copper (Cu), aluminum (Al),tungsten (W), alloys of these metals, and other similar metals. Thesematerials may be deposited by conventional deposition processesincluding, but not limited to a CVD process and an electrochemicalprocess like electroplating or electroless plating.

With continued reference to the FIGURE, the conductive plates 20, 22 inmetallization layer 14 are clad on two sides (i.e., the upper and lowersides) by regions of barrier layers 60, 61, respectively. The lateralsides of the conductive plates 20, 22 are in direct physical contactwith dielectric material in insulating layer 24. Similarly, theconductive plates 26, 28 in metallization layer 16 are clad on two sidesby barrier layers 62, 63, respectively. The lateral sides of theconductive plates 26, 28 are in direct physical contact with dielectricmaterial in insulating layer 30. In contrast, the conductive plates 44,46 are clad on three sides by barrier layer 64 so that only one side(i.e., the upper side) is in direct physical contact with dielectricmaterial in insulating layer 50.

Conductive plates 20, 22 may be formed using a standard lithography andsubtractive etching process to pattern a metal stack deposited oninsulating layer 32, after the conductive plugs 34, 36 are fabricated.The metal stack includes barrier layer 61, such as a bilayer of titaniumand titanium nitride, a layer of a metal, such as aluminum, and barrierlayer 62, such as another bilayer of titanium and titanium nitride.Conductive plates 20, 22 may be defined from the metal stack by applyinga resist layer (not shown), patterning the resist layer, anisotropicallyetching the metal stack using, for example, a reactive ion etching (RIE)process, capable of producing substantially vertical sidewalls, andstripping residual resist from the conductive plates 20, 22 by, forexample, plasma ashing or a chemical stripper. Insulating layer 24 isdeposited as a gap fill material and polished to a substantially planarcondition by, for example, a chemical mechanical polishing (CMP)process. Conductive plates 26, 28 are formed in insulating layer 30 by asimilar procedure as the procedure forming conductive plates 20, 22.

Conductive plates 44, 46 may be formed in insulating layer 48 by aconventional single damascene process. After insulating layer 48 isdeposited, troughs are formed in the insulating layer 48 using aconventional lithography and etching process. A resist layer (not shown)is applied to cover insulating layer 48, is exposed to impart a latentimage pattern of the troughs, and is developed to transform the latenttrench image pattern into a final image pattern with unmasked areas thatexpose insulating layer 24 at the future locations of the troughs.Troughs with substantially vertical sidewalls are defined in theunmasked area of insulating layer 48 with an etching process, such asplasma etching or RIE. After the etching process is concluded, residualresist is stripped from insulating layer 48 by, for example, plasmaashing or a chemical stripper.

In an alternative embodiment, the vias for conductive plugs 55, 56 andthe troughs for conductive plates 44, 46 may comprise a dual-damascenepattern formed by a via-first, trough-last process sequence or atrough-first, via-last process sequence. The ability to perform dualdamascene process steps regardless of order is familiar to a personhaving ordinary skill in the art.

The barrier layers 60-64 may include any material or multilayercombination of materials recognized by a person having ordinary skill inthe art. Exemplary materials for barrier layers 60-64 include, but arenot limited to titanium (Ti), titanium nitride (TiN), tantalum (Ta),tantalum nitride (TaN), combinations of these materials, and other likematerials. The material constituting barrier layers 60-64 may be formedutilizing conventional deposition processes well known to those skilledin the art, including but not limited to PVD, ionized-PVD (iPVD), atomiclayer deposition (ALD), CVD, and plasma-assisted CVD.

The conductive plates in the other metallization layers (not shown) mayhave a construction analogous to the construction of conductive plates20, 22 and conductive plates 26, 28, or may have a constructionanalogous to the construction of conductive plates 44, 46.

Additional process steps are performed to provide electrical connections(not shown) to the conductive plates 20, 22, 26, 28, 44, 46 of the VPPcapacitor structure 10. Specifically, an electrical connection for usein electrically biasing at least one of the conductive plates 20, 26, 44with a potential having one polarity (e.g., positive) and anotherelectrical connection for use in electrically biasing at least one ofthe conductive plates 22, 28, 46 with a potential having the oppositepolarity (e.g., negative). The conductive plugs 34, 38, 52, 55electrically couple conductive plates 20, 22, 26, 28, 44, 46 and,optionally, other overlying and underlying conductive plates (notshown). Similarly, the conductive plugs 36, 40, 54, 56 electricallycouple conductive plates 22, 28, 46 and optionally other overlying andunderlying conductive plates (not shown). The process steps may besubsumed by the process steps forming the conductive plates 20, 22, 26,28, 44, 46.

Conductive plates 20, 26, 44 are generally aligned in one verticalcolumn, which is biased with one polarity, and conductive plates 22, 28,46 are generally aligned in another vertical column, which is biasedwith the opposite polarity. Conductive plates may be provided inadditional columns adjacent to the column containing conductive plates20, 26, 44 and/or to the column containing conductive plates 22, 28, 46.Independent of the number of columns of conductive plates, the biaspotential for the columns alternates between the different polarities sothat conductive plates in adjacent columns of the VPP capacitorstructure 10 are biased with opposite polarities.

With continued reference to the FIGURE, conductive plates 20, 22, aswell as other adjacent pairs of conductive plates (not shown) inmetallization layer 14, have confronting sides 70, 72, respectively,spaced apart by first dielectric-filled gap characterized by a firstdistance, W₁. The dielectric material filling the gap originates frominsulating layer 24. Similarly, conductive plates 26, 28, as well asother adjacent pairs of conductive plates (not shown) in metallizationlayer 16, have confronting sides 74, 76, respectively, that are spacedapart by a dielectric-filled gap characterized by a second distance, W₂.The dielectric material filling the gap originates from insulating layer30. Conductive plates 44, 46, as well as other adjacent pairs ofconductive plates (not shown) in metallization layer 18, haveconfronting sides 78, 80, respectively, that are spaced apart by adielectric-filled gap characterized by a third distance, W₃. Thedielectric material filling the gap originates from insulating layer 48.The first, second, and third distances are selected to differ from eachother so that the conductive plates 20, 22, the conductive plates 26,28, and the conductive plates 44, 46 are formed with unique pitches. Inan alternative embodiment, only two of the first, second, and thirddistances may differ. Adjacent conductive plates (not shown) inmetallization layers (not shown) either overlying or underlyingmetallization layer 18 may be spaced by distances selected from amongthe first, second, and third distances, or by one or more additionaldistances distinct from first, second, and third distances.

Conductive plates 20, 22 may be formed from the same material (e.g.,aluminum or aluminum alloy) as conductive plates 26, 28. Alternatively,conductive plates 20, 22 may be formed from a different material (e.g.,copper or copper alloy) than conductive plates 26, 28 (e.g., aluminum oraluminum alloy). Similarly, conductive plates 44, 46 may be formed froma different material (e.g., copper or copper alloy) than conductiveplates 26, 28 (e.g., aluminum or aluminum alloy) or from the samematerial as conductive plates 26, 28. Similar considerations apply forthe selection of materials forming the conductive plates in overlyingand underlying metallization layers (not shown).

Conductive plates 20, 22 in metallization layer 14 may be alignedsubstantially parallel to each other with top and/or bottom surfacescontained in respective substantially horizontal planes. Similarly,conductive plate 26 may be aligned substantially parallel withconductive plate 28 with top and/or bottom surfaces contained inrespective substantially horizontal planes, and conductive plates 44, 46may be aligned substantially parallel with each other with top and/orbottom surfaces contained in respective substantially horizontal planes.Alternatively, one or more of the horizontal plate alignments in each ofthe metallization layers 14, 16, 18 may vary from parallel.

In one embodiment, conductive plate 20 in metallization layer 14directly overlies conductive plate 26 in metallization layer 16 andconductive plate 44 in metallization layer 18. Similarly, conductiveplate 22 in metallization layer 14 may directly overlie conductive plate28 in metallization layer 16 and conductive plate 46 in metallizationlayer 18. Alternatively, conductive plates 20, 22 may be shiftedhorizontally relative to conductive plates 26, 28 and/or conductiveplates 26, 28 may be shifted horizontally relative to conductive plates44, 46 so that direct vertical alignment is relaxed, while maintainingthe pitch or spacing between adjacent plate pairs in the differentmetallization layers 14, 16, 18.

In an alternative embodiment, the metallization layers 14, 16, 18 mayalso contain a multilevel interconnect structure, which is generallyindicated by reference numeral 90. The interconnect structure 90, whichis formed by the BEOL processes, interconnects the various circuitsand/or devices (not shown) formed on substrate 12 by front end of line(FEOL) processes, electrically contacts features on substrate 12, andalso provides connections to external contacts (not shown).

Metallization layer 14 may further include a plurality of conductivelines, of which conductive line 92 is representative, that are formed ininsulating layer 24 and are clad by portions of barrier layers 60, 61.The underlying metallization layer 16 may also include a plurality ofconductive lines, of which conductive line 94 is representative, thatare formed in insulating layer 30 and are clad by portions of barrierlayers 62, 63. Conductive plugs, such as the representative plug 96,fill vias defined in insulating layer 32 and, thereby, supply verticalconnections between the conductive lines 92, 94. Conductive plugs, suchas the representative plug 98, fill vias defined in insulating layer 42and, thereby, supply vertical connections between conductive lines 92and an optional overlying conductive line (not shown) in an overlyingmetallization layer.

Metallization layer 18 also includes a plurality of conductive lines, ofwhich conductive line 99 is representative, that are formed ininsulating layer 48. The conductive line 99 is isolated from insulatinglayers 48, 58 by barrier layer 64. Conductive plugs, such as therepresentative plug 100, fill vias defined in insulating layer 50 tosupply vertical connections between the conductive lines 94, 99.Conductive plugs, such as the representative plug 102, fill vias definedin insulating layer 58 and, thereby, supply vertical connections betweenconductive line 99 and an optional underlying conductive line (notshown) in an underlying metallization layer.

References herein to terms such as “vertical”, “horizontal”, etc. aremade by way of example, and not by way of limitation, to establish aframe of reference. The term “horizontal” as used herein is defined as aplane parallel to a conventional plane of a semiconductor substrate,regardless of its actual three-dimensional spatial orientation. The term“vertical” refers to a direction perpendicular to the horizontal, asjust defined. Terms, such as “on”, “above”, “below”, “side” (as in“sidewall”), “upper”, “lower”, “over”, “beneath”, and “under”, aredefined with respect to the horizontal plane. It is understood thatvarious other frames of reference may be employed for describing theinvention without departing from the spirit and scope of the invention.

The fabrication of the semiconductor structure herein has been describedby a specific order of fabrication stages and steps. However, it isunderstood that the order may differ from that described. For example,the order of two or more fabrication steps may be switched relative tothe order shown. Moreover, two or more fabrication steps may beconducted either concurrently or with partial concurrence. In addition,various fabrication steps may be omitted and other fabrication steps maybe added. It is understood that all such variations are within the scopeof the invention. It is also understood that features of the inventionare not necessarily shown to scale in the drawings. Furthermore, to theextent that the terms “includes”, “having”, “has”, “with”, or variantsthereof are used in either the detailed description or the claims, suchterms are intended to be inclusive in a manner similar to the term“comprising.”

While the invention has been illustrated by a description of variousembodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Thus, the invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicants' general inventive concept.

1. A capacitor structure comprising: a first plurality of conductiveplates, the first plurality of conductive plates spaced apart by a firstdistance; and a second plurality of conductive plates having anoverlying relationship with the first plurality of conductive plates,the second plurality of conductive plates spaced apart by a seconddistance different than the first distance.
 2. The capacitor structureof claim 1 wherein the first plurality of conductive plates comprise afirst material, the second plurality of conductive plates comprise asecond material, and the first material is the same as the secondmaterial.
 3. The capacitor structure of claim 1 wherein the firstplurality of conductive plates comprise a first material, the secondplurality of conductive plates comprise a second material, and whereinthe first material is different than the second material.
 4. Thecapacitor structure of claim 3 wherein the first material containscopper, the second material contains aluminum, and the second distanceis greater than the first distance.
 5. The capacitor structure of claim1 wherein the first plurality of conductive plates are alignedsubstantially parallel to each other, and the second plurality ofconductive plates are aligned substantially parallel to each other. 6.The capacitor structure of claim 1 wherein one of the second pluralityof conductive plates directly overlies a respective one of the firstplurality of conductive plates and is physically coupled with therespective one of the first plurality of conductive plates.
 7. Thecapacitor structure of claim 6 further comprising: a plurality ofconductive plugs each coupling one of the first plurality of conductiveplates to a respective one of the second plurality of conductive plates.8. The capacitor structure of claim 1 wherein adjacent pairs of thefirst plurality of conductive plates and adjacent pairs of the secondplurality of conductive plates are separated by dielectric material toprovide electrical isolation.
 9. The capacitor structure of claim 1further comprising: an insulating layer between the first plurality ofconductive plates and the second plurality of conductive plates.